On a long-term basis, hydrogen is an important carrier for a sustainable energy supply. Today, most of the hydrogen is prepared from fossil sources. However, the limited presence of these sources and the indispensable reduction of greenhouse gases (mainly CO2) require the exploration of alternative resources or processes. Water splitting by means of electrolysis using solar current is possible, but has the disadvantage of an enormous influence of the cost of solar current on H2 production. The direct utilization of concentrated solar radiation for thermochemical water splitting avoids this and has a higher efficiency. Thus, the cost of hydrogen production can be lowered and production on an industrial scale enabled on a long-term basis.
A number of processes are available for the thermal production of hydrogen.
Thus, in DE 44 10 915 A1, hydrogen is produced by the reaction of iron with carbonic acid with supply of solar-thermal energy. The iron oxide formed is reduced again using carbon monoxide and is thus available for the process.
In DE 42 26 496 A1, hydrogen is produced in a modified continuous iron-water vapor process, and the iron oxide formed thereby is subsequently supplied to steel production again.
JP 03205302 A describes the preparation of highly pure hydrogen using activated magnetite as a reactive catalyst.
In JP 2001270701 A, hydrogen is prepared by reacting metallic zinc, magnetite and water at 600° C.
M. Inoue et al. in Solar Energy (2003) describes the preparation of hydrogen by means of a water-ZnO—MnFe2O4 system. The corresponding ferrite powder of the type Mex2+Zn1−x2+Fe2O4 can be prepared by the method of S. Lorentzou et al. as presented on the conference Partec 2004.
According to a press communication by the Deutsches Zentrum für Luft- and Raumfahrt of Oct. 15, 2004, hydrogen was produced for the first time in a solar oven by solar-thermal water splitting. In the process described, the hydrogen is produced discontinuously by splitting the water vapor over metal oxide and regenerating the metal oxide.
DE 197 10 986 C2 describes a volumetric radiation receptor for heat recovery from concentrated radiation by heating a fluid under pressure without a chemical reaction occurring in this reactor.